Adhesive label

ABSTRACT

An adhesive label comprising, in order, a printing carrier, a primer on the back of the printing carrier, an adhesion layer, a covering layer, and an optional adhesive-repellent layer between the adhesion layer and the cover layer. The primer comprises isocyanate-terminated compounds, particularly isocyanate-terminated polyurethanes. The adhesive label is made by applying the adhesion layer to the covering layer or to the optional adhesive-repellent layer on the covering layer, and combining the adhesion layer and a stratum made from the printing carrier and the primer by applying the adhesion layer onto the primer.

FIELD OF THE INVENTION

The invention relates to an adhesive label, consisting of a printingcarrier, a primer on the back of the printing carrier, a layer ofadhesive on the side of the primer oriented away from the printingcarrier, a covering layer on the side of the adhesion layer orientedaway from the primer and, if required, of an adhesive-repellent layerbetween the adhesion layer and the cover layer, the adhesion layerpreferably being removable. The invention further relates to anespecially effective method for the manufacture of an adhesive label inwhich the primer is applied to the back of the printing carrier.

BACKGROUND OF THE INVENTION

Adhesive labels of the type under discussion have basically been knownfor a long time (see German Laid-open Applications DE-OS No. 34 17 746,25 46 108 and 15 94 060). Adhesive labels which can be removed again,i.e., which can be removed after having been glued on once, make specialdemands on the chemical composition of the several layers of such anadhesive label, especially on the chemical composition of the adhesionlayer. The printing carrier, which can consist of many types ofmaterial, though mostly of paper, and which represents the real surfaceof the adhesive label, in most cases can only be mechanically stressedto a limited degree and therefore requires the adhesion layer to have alow peeling value. At the same time, the adhesion layer must optimallystick on the substrate on which it is glued. The material of theadhesion layer must, on the one hand, be very free-flowing in order topeel off an adhesive label with as little residue as possible, and, onthe other hand, the material must also show good internal cohesion. Thepeeling value also should not be permitted to increase too much inrespect to the duration of adhesion, but should optimally be as constantas possible. Finally, the adhesion of the adhesion layer to the printingcarrier must be greater than to the substrate on which it is glued,regardless of good adhesion to the substrate on which it is glued.

It is precisely the special demands for a removable adhesive label thathave led to a special interest being given to the primer attached to theback of the printing carrier. In the final analysis, the previouslynoted requirements make considerable demands on this primer. The stateof the art works with a primer applied in the liquid phase which, afterbrief initial drying, is covered with the adhesive of the adhesivelayer, also sill in the liquid phase. Primer as well as adhesive arematerials dissolved in highly volatile liquid hydrocarbon solvents.

A special problem of the known adhesive labels is their tendency to agebecause of migration of molecules from the adhesive layer into theprinting carrier and because of chemical changes in the adhesive layer.A further considerable problem is the use of environmentally burdensomesolvents for the primer and adhesives of the adhesive layer. Finally,the cost effectiveness of the known removable adhesive labels is not yetsatisfactory.

SUMMARY OF THE INVENTION

The entire object of the teaching of the invention is the improvement ofthe known adhesive label described above from the standpoint of theproduct and its manufacture in regard to subsequent removal, resistanceto aging, ease of manufacture, environmental compatibility and costeffectivess.

The adhesive label of the invention in which the above object has beenachieved is characterized in that the primer consists ofisocyanate-terminated (NCO-terminated) solvents. It is especiallyadvantageous if the primer consists of isocyanate-terminatedpolyurethane. However, other isocyanate-terminated compounds are alsoconceivable, for example, isocyanate-terminated natural rubber.

In accordance with the invention, it has been realized that the materialof the primer of an adhesive label of the type in question has adecisive importance, especially with a view to its subsequent removal.Especially the chemical reactions between the printing carrier, theprimer and the adhesive, taking into consideration the hardening of theprimer over time, lead to the desired effective anchoring of theadhesive layer in the printing carrier and to the desired bonding of theadhesive label.

The invention assigns special importance to the manufacture of theprimer from isocyanate-terminated compounds, especially fromisocyanate-terminated polyurethane. For low-molecular isocyanatepolyurethanes the following general reaction formula is valid: ##STR1##

The following formula for a polyether diol as a residual group isobtained: ##STR2##

This is only an example for a particular residual group, the values forn and x also being variable within a wide range here. It is ofimportance that with isocyanate-terminated compounds the addition ofwater from the air or from the paper used as the printing carrier leadsto the formation of polycarbamide derivatives resulting in high-gradelinking. In parallel, bonding with functional groups of the printingcarrier and the adhesive layer (OH group, COOH group, NH₂ group, etc.)takes place, resulting in an active anchoring of the terminatingisocyanate groups of the primer.

Additional fillers can be used for the modification of the properties ofthe primer. It is especially recommended to add a highly dispersed,pyrogenic, especially water-repellent silicic acid to the primer as afiller, preferably made water-repellent by means ofdichlorodimethylsilane. The fluidity properties of the primer and itshardening reaction can be influenced by these fillers.

Of special importance in regard to environmental compatibility is thefact that isocyanate-terminated compounds, especiallyisocyanate-terminated polyurethane, can be easily manufactured withoutsolvents. Such a primer free of solvents can easily be worked inapplication devices which are customary with solvent-free laminatingadhesives.

Tests have shown that for the primer to be used with an adhesive labelaccording to the invention an application weight between 1.0 and 5.0g/m², preferably between 1.5 and 2.5 g/m², especially approximately 2.0g/m², is recommended. Even if the primer is solvent-free, it need not beprotected from moisture in the air. Application of the primer shouldtake place at a temperature between approximately 90° and 100° C.,preferably at approximately 95° C. A standard application device can beused for this application.

Normally, hardening of the primer used in the invention for an adhesivelabel of the type under discussion will take place in about a week.After hardening, the danger of migration of molecules of the adhesiveinto the printing carrier is extremely low. Because of the choice andstandardization of the primer in accordance with the invention it isachieved that even during the hardening time, no significant migrationof molecules of the adhesive into the printing carrier take place. Onthe contrary, the reactive bonding via the terminal-position isocyanategroups takes place here in the manner discussed in detail above.

All sorts of adhesives are suitable for the adhesive layer, i.e., thereare no restrictions in regard to the type of the adhesive, the method ofapplication and the application device. Adhesives containing solvents,dispersion adhesives, hot melting adhesives and/or adhesives that areliquid at room temperature, etc. can be used. The consideration ofworkability, environmental compatibility and, of course, the generalconsideration of subsequent removal are of special importance for theadhesive layer. Especially considering environmental compatibility,polyacrylate (acrylate copolymer), dispersed in water, is recommended asadhesive. For such an adhesive it is recommended that the dryapplication weight of the adhesive layer be approximately 17 to 23 g/m²,preferably approximately 18 to 22 g/m², especially approximately 20g/m².

A natural rubber adhesive has proven effective in tests as an adhesivedissolved in a solvent and has shown good results especially withgasoline as a solvent. In this case a dry application weight of 18 to 26g/m², preferably between 20 and 24 g/m², especially approximately 22g/m², is recommended.

In general it is true in the selection of the adhesive layer that itmust have a sufficient number of hydrogen atoms for the generation ofreactive bonds with the primer and that the adhesive propertiesespecially fulfill the requirement of subsequent removability. In thisrespect it must be noted that the properties of the primer present inaccordance with the invention generally result in the adhesive layerbeing somewhat harder than expected after the hardening process, basedon the basic chemical composition--a result of the reactive bond withthe primer.

Regarding the cover layer for the adhesive label according to theinvention, it is recommended to manufacture it, together with theadhesive-repellent layer, of silicon paper, an outstanding solution inregard to workability and cost effectiveness.

Excellent results are achieved with the adhesive label according to theinvention which regard to subsequent removal, since the bonding effectcreated by the primer favors a smooth peel-off of the adhesive layerfrom the substrate on which it is glued. The aging properties of theadhesive label are excellent because of the blocking function of theprimer of the type according to the invention. Workability is improvedsince the adhesive label can be easily cut or perforated because of theexcellent anchoring of the several layers by the primer, without theadhesive layer exuding from the cut or perforated places, so thatfurther treatment--cutting into rolls, guillotine cutting, stamping outof labels--is easily possible. The use of materials free of solventsresults in an excellent environmental compatibility and, at the sametime, has a beneficial influence on cost effectiveness.

It was explained in the beginning that the teaching of the invention isalso directed to an improved method for manufacturing an adhesive labelof the type under discussion. The previously stated object is attainedin that the adhesive layer is applied on the cover layer or theadhesive-repellent layer combined with the adhesive layer, in that, ifrequired, then the adhesive layer is pre-dried and in that afterwardsthe strata made from the cover layer, the adhesive-repellent layer, ifpresent, and the adhesive layer and the stratum made from the printingcarrier and primer is combined over its entire surface by placing theadhesive layer on the primer. In accordance with the invention it wasrealized that the adhesive layer, whether with an adhesive dissolved ina solvent or with an adhesive dispersed in water, is especiallyeffectively dried together with the cover layer and should only then,after reaching an exactly predetermined degree of dryness, be broughtinto contact with the primer. It is possible by means of the methodaccording to the invention for the primer, applied on the inside of theprinting carrier, itself to have an exactly predetermined optimal degreeof dryness so that the common further hardening of the primer and theadhesive layer together can be exactly predetermined. In the state ofthe art from which the teaching of the invention proceeds only aprevious and defined pre-drying of the primer, but not of the adhesivelayer, was possible. In contrast to this it becomes possible with themethod according to the invention to additionally and particularlyinfluence the migratory ability of the molecules of the adhesive layerby means of pre-drying prior to the adhesive layer being brought intocontact with the primer.

At the same time an improved workability of the adhesive layer isachieved with the method according to the invention by using theexcellently manipulable cover layer, practically inverted, as a supportfor the adhesive layer.

Altogether the method according to the invention makes it possible tocreate an adhesive label considerably improved with respect tosubsequent removal and aging resistance while at the same timeproceeding without manufacturing problems and with cost effectiveness.

With regard to the method, it is recommended to proceed such that themethod steps regarding the application of the adhesive layer take placefirst and that the combination of the two strata take place immediatelyafter the application of the primer to the printing carrier. The timeinterval for the primers used in accordance with the invention isoptimally set at 1 to 5 s, preferably at 2 to 3 s.

Especially these times fixed in accordance with the preferred teachingof the invention make clear that working within the framework of themethod according to the invention is completely different from the stateof the art.

According to the early course of hardening with regard to the primer,i.e., the anchoring process within the first 24 hours, as explainedabove, it is recommended to store the adhesive label material, forexample, rolled up, for 16 to 24 hours prior to further treatment, i.e.before cutting or perforating it to form individual adhesive labels.

The invention is again briefly described below by means of the drawingsshowing only one exemplary embodiment. Two exemplary embodiments areadditionally given as numerical examples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic and cross-sectional view of an adhesive labelaccording to the invention prior to the last method step ofmanufacturing, and

FIG. 2 is the adhesive label after the last method step ofmanufacturing.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1 and 2 give a good view of the composition of the adhesive labelin accordance with the teaching of the invention and in the exemplaryembodiment here shown consists of a printing carrier 1, a primer 2 onthe backside of the printing carrier 1, an adhesive layer 3 on the sideof the primer 2 oriented away from the printing carrier 1, a cover layer5 on the side of the adhesive layer 3 oriented away from the primer 1and, in the exemplary embodiment shown here, also of anadhesive-repellent layer 4 between the adhesive layer 3 and the coverlayer 5. In the preferred exemplary embodiment here shown the adhesivelayer 3 is to be a subsequently removable layer, i.e. to be subsequentlyremovable from a substrate, not shown here, on which it is to be gluedand on which it was previously pressed.

In the preferred exemplary embodiment shown here the primer 2 consistsof an isocyanate-terminated polyurethane with highly dispersed,pyrogenic and water-repellent silicic acid as filler. The adhesive layer3 consists of polyacrylate dispersed in water. The application weight ofthe primer 2 is around 2.0 g/m², that of the adhesive layer 3 around 20g/m². FIG. 1 shows the state in which the strata made of adhesive layer3, adhesive-repellent layer 4 and cover layer 5 have been made and inwhich the adhesive layer 3 already has been pre-dried. In contrastthereto the stratum made from printing carrier 1 and primer 2 has justnow been prepared, i.e. approximately 2 seconds ago. The primer 2therefore is only slightly pre-dried and now is brought, as shown inFIG. 2, into full contact over its entire area with the adhesive layer3.

In FIG. 2 it is indicated by dashed boundary lines that by use of theprimer 2 according to the invention, a reactive bonding of the primer 2to the printing carrier 1 on the one side and to the adhesive layer 3 onthe other takes place. If the cover layer 5 with the adhesive-repellentlayer 4 is removed at a later time, for example after the hardening timeof the primer 2 of a week, and the adhesive label is stuck on asubstrate, the adhesive label can be loosened relatively easily because,on the one hand, the adhesive layer 3 permits renewed removal and, onthe other, the adhesive layer 3 has a close bond with the printingcarrier 1 via the primer 2.

In a first numerical example the printing carrier 1 consists of labelpaper 80 g/m². A siliconed glassine paper serves as cover layer 5 withadhesive-repellent layer 4. The printing carrier 1 is coated on itsbackside, with the aid of a roller applicator device, at 95° C. with theprimer 2 which, in this case, is a solvent-free laminated resin. Theapplication weight is about 2 g/m². Within 2 to 3 seconds after theapplication of the primer 2 the previously manufactured and pre-driedstrata made of adhesive layer 3, adhesive-repellent layer 4 and coverlayer 5 is applied. The viscosity of the primer 2 at this point in theprocess lies, depending on the phase, between 1,200 and 2,200 mPas, inthis case approximately 2,000 mPas.

The adhesive layer 3 in the exemplary embodiment described here is a 51%aqueous dispersion with a dry application weight of about 20 g/m².Account is taken of the additional hardening to be expected because ofthe primer 2 in the adhesive layer 3 by admixing 5% softener to the dryweight.

Stable adhesive values have been reached after about a week with thebonding structure previously explained. The adhesive label is veryresistant to aging and can be relatively easily loosened from asubstrate even after a long time.

In the second example another adhesive layer 3, namely with asolvent-containing adhesive having a dry application weight of about 22g/m², is used with the primer 2 remaining the same. After evaporation ofthe solvent the same processing as in the previous exemplary embodimentwas used.

It is to be understood that the above described exemplary embodiments ofthe invention have been given by way of example only and that furthervariants and improvements are possible within the scope of theinvention.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingcurrent knowledge, readily modify and/or adapt for various applicationssuch specific embodiments without departing from the generic concept,and therefore such adaptations and modifications are intended to becomprehended within the meaning and range of equivalents of thedisclosed embodiments. It is to be understood that the phraseology orterminology employed herein is for the purpose of description and not oflimitation.

What is claimed is:
 1. An adhesive label comprising the following layersin order:a printing carrier; a primer consisting essentially of asolvent-free, isocyanate-terminated polyurethane and a highly dispersed,pyrogenic, silicic acid filler; an adhesion layer consisting essentiallyof a polyacrylate dispersed in water; and a cover layer; wherein dryapplication weight of said adhesion layer is from about 17 to about 23g/m².
 2. The adhesive label of claim 1 wherein said silicic acid hasbeen rendered water-repellent by dichlorodimethylsilane.
 3. The adhesivelabel of claim 1 wherein the application weight of the primer rangesfrom about 1.0 to about 5.0 g/m².
 4. The adhesive label of claim 1wherein the primer is applied at a temperature ranging from about 90° to100° C.
 5. The adhesive label of claim 1 wherein the dry applicationweight of the adhesion layer is approximately 18 to 22 g/m².
 6. Theadhesive label of claim 5 wherein the dry application weight of theadhesion layer is approximately 20 g/m².
 7. The adhesive label of claim1 wherein the cover layer is made of silicon paper.